The present invention broadly relates to the separation of a gas from a liquid. It particularly relates to an apparatus for the separation of a noncondensable gas from liquid metal in a zero gravity environment.
There is currently a major, combined effort being made by certain government agencies to develop a high-power, light-weight nuclear reactor power source (SP-100 Reactor) for use on future spacecraft. The program will require the resolution of numerous technological challenges. One of those challenges will be to provide a means for removing tritium and helium gas from the reactor coolant.
The SP-100 Reactor utilizes liquid lithium as the reactor coolant and heat transport medium. Under neutron irradiation (which occurs inside the reactor core) lithium fissions into tritium and helium atoms which form molecules of gas. The amount of gas generated under such circumstances can be reduced by using lithium which is enhanced in the isotope Li-6; however, even Li-6 fissions at a rate such that approximately one liter of gas would be generated in the coolant per year of operation at 100 KWa (net). This gas must be removed and maintained separate from the coolant. If it were allowed to accumulate it would interfere with the heat transport of the coolant and could result in overheating and failure of individual fuel pins within the reactor core. Furthermore, the reactor must continue to be cooled via circulation of the coolant for several years after ultimate shut-down or failure of the system in order to remove the heat of radioactive decay of fission products. Thus there must be provided some means for maintaining the gas separate from the liquid coolant which would continue to function reliably even after loss of electrical power and loss of control over the gas separation apparatus.
Removing entrained gas bubbles from a liquid metal in a zero gravity environment is not an easy task. In the absence of a gravity gradient, the gas could be anywhere in the system. Nonetheless it is essential that some means be provided for separating the gas from the coolant and accumulating it in a continuous manner. Using moving parts such as a centrifugal pump which could separate liquid from a gas via centripetal acceleration would not be satisfactory due to reliability concerns; namely, mechanical devices can fail.
In addition, once separated there also must be some means for keeping the gas separate from the liquid coolant. Venting the gas into open space would not be acceptable if valves were required since a valve failure (either open or closed) could result in overheating of the reactor core with the attendant loss of the power system. A gas permeable frit could be used to form a portion of the wall in the coolant system. The permeable frit would let the gas diffuse out of the system into space. This would be undesirable, however, because it would represent a structurally weak point in the coolant system. Accordingly, there should be some means of storing the gas in the system which would be capable of maintaining the gas and liquids separate throughout the life of the system.